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CDC reports 2 trichinellosis outbreaks traced to walrus meat

Federal officials this week made public details of two outbreaks of Trichinella infections in Alaska in the past 12 months, both linked to undercooked walrus meat.

Long associated with undercooked pork, the majority of cases of Trichinella infections in the U.S. since the late 1990s have been caused by wild game species that are not in the porcine, or pig, family, according to a report posted Thursday by the Centers for Disease Control and Prevention.

“These were the first multiple-case outbreaks of walrus-associated trichinellosis in Alaska since 1992,” the CDC reported Thursday.

“These outbreaks highlight the importance of culturally sensitive public health messaging. In areas where wild game species are harvested for subsistence, traditional methods of collecting, handling, preparing, storing, and consuming meat often have great cultural significance; however, some of these methods can be inconsistent with public health best practices.”

The two outbreaks, with illnesses reported from July 2016 through May this year, sickened a total of 10 children and adults, all of whom have recovered.

Ironically the outbreak this spring came amidst a public service campaign by Alaskan public health officials specifically timed to raise awareness during the spring walrus hunts. Alaska Natives have the right under federal law to harvest the large marine mammals. The hunts are part of indigenous cultures’ traditions and the meat is used for subsistence by many Alaska Natives.

A traditional method of cooking walrus meat is to boil it until the exterior is cooked but the interior is undercooked or raw. Outbreak victims interviewed by public health officials reported that many members of native communities prefer the taste and texture of undercooked or raw walrus meat to that of fully cooked meat, according to the CDC report.

“… the parasite cannot be reliably killed by smoking, drying, or fermenting meat, and the arctic species Trichinella nativa is freeze tolerant,” according to the CDC’s report.

Although wild game meat is a well known source of the larvae of a microscopic ringworm called Trichinella spiralis, the illnesses liked to walrus in the past 12 months are somewhat of a mystery for investigators at the CDC and the Alaska Division of Public Health.

About 94 percent of the 241 trichinellosis cases reported in Alaska since 1975 were attributed to consumption of non-porcine wild game, including black bear, grizzly bear, polar bear, walrus and sea ice–associated seal species the CDC reported.

Since 1975, 100 of the 241 trichinellosis cases in the state have been associated with walrus meat and another 24 were linked to walrus or seal meat.

“However, the frequency of walrus-associated trichinellosis in Alaska has declined sharply in recent years from an average of 6.3 cases per year — 113 cases over 18 years during 1975-1992 — to an average of 0.5 cases per year (for) 11 cases over 24.5 years during 1993-2017, as of July 1,” according to the CDC report.

“Reasons for this decline in incidence are unknown and might involve changes in parasite burden in walruses; the timing or location of walrus hunting; methods used to store, collect, handle, or prepare walrus meat for consumption; reporting practices among ill persons; and clinical testing methods or practices.”

Anyone who has eaten undercooked wild game meat and developed symptoms of infection from the Trichinella parasite should seek medical attention and tell their doctors about the possible exposure.

Early symptoms occur one to two days after ingestion of contaminated meat and include diarrhea, abdominal pain, fatigue, nausea and vomiting. Systemic symptoms typically occur one to two weeks after ingestion and last for one to eight weeks. Systemic symptoms include facial and eye edema, fatigue, fever and chills, headache, muscle soreness, severe skin itching with or without a rash, nausea, difficulty coordinating movement, neurologic complications, and cardiopulmonary impairment.

“These outbreaks underscore the importance (of health care providers) inquiring about consumption of commercially prepared and personally harvested meats, and about methods of meat preparation, when evaluating suspected trichinellosis cases, especially in areas where consumption of wild game in association with recreational or subsistence hunting is common,” the CDC researchers reported.

“Rather than promoting or proscribing specific methods, public health messages that focus on communicating risks and explaining the manner and magnitude of risk reduction that can be achieved using different approaches, e.g., alternative methods of preparing meat for consumption, enable members of the target population to make informed decisions that integrate their traditional practices with their awareness and tolerance of risks.”